Intensity-modulated radiation therapy (IMRT) is a treatment method for accurately delivering a defined and uniform dose of radiation to a tumor site. This treatment method is designed to limit the amount of radiation to which peripheral non-cancerous tissues and structures are exposed. IMRT is used on cancer patients to deliver a uniform dose of radiation to a patient's cancerous tissue as defined by the clinician while avoiding, or at least minimizing, radiation exposure to the surrounding healthy or critical body structures of the patient. IMRT delivers radiation to the patient's cancerous tissue from various angles and at various intensity levels in order to achieve the prescribed dose profile for that patient. Patients with cancer can be treated with other types of radiation therapy such as proton radiation therapy or cobalt radiation therapy.
With IMRT and other types of radiation therapy, the intensity of the radiation beam can be varied or modulated by using a compensator. A compensator is also known as a radiation filter. The compensator is mounted directly in the path of a radiation beam generated by a radiation therapy machine, before the beam reaches the patient. Each compensator is made specifically for a particular patient and also for each angle (field) from which radiation is delivered. Existing practice utilizes compensators machined from a solid piece of material. The unique patient-specific three-dimensional geometry of each machined finished compensator provides the conformal radiation dose distributions required by that particular cancer patient to treat their tumor according to the prescribed dose. In general, a compensator created for one cancer patient cannot effectively be used for the treatment of another cancer patient. Individual compensators are used from each beam angle (field) during a course of IMRT treatment, requiring a change of compensator for each discrete field of radiation treatment. Compensators are typically provided in “sets” for a treatment plan for a specific patient.
Patient-specific compensators can be machined in-house at a hospital or other radiation treatment facility, or the compensators can be ordered from a 3rd party supplier such as an outside machine shop. One outside machine shop from which compensators can be ordered is .decimal, Inc of Sanford, Fla. (www.dotdecimal.com). After manufacturing the ordered compensator, the outside machine shop physically delivers that set of compensators to the requesting treatment facility, typically by shipping it to the facility using a general carrier.
Before any compensator is mounted to a radiation therapy machine and used in the radiation treatment of an actual patient, the compensator must be validated in a quality assurance (QA) process. If the compensator does not pass the QA check, it will not be used in the radiation treatment of a cancer patient.